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ORIGIN OF PERISSODACTYLES

199

canines would in the same way cease to be useful, and even
become encumbrances to such grazing creatures; and their dis-
appearance is one of the salient features in the history of the
Vngulata, that is of the modem representatives of the order. The
extraordinary hypertrophy of these teeth in such a line as that of
the Amblypoda, which has left no descendants, was one of the
reasons perhaps for the decay of those great pachyderms of znid-
Terfciary times ; their excessive armature became an encumbrance,
since it was not accompanied by improvements in other necessary

Fie, IIS.  Boixes of the mantis A, of Rhinoceros, li/tiiboeeros sumatrensis.

Pig, Sus scrqfa.     x |.     Letters  as in Fig. 112.     (From Mower's

B, of

directions. Some of the features of the Tertiary Ungulates have,
however, been dealt with in our general sketch of the mammalian
life during that epoch, and need not be again referred to here. Of
existing Ungulates there are no clear indications of the descent of
the Elephants or of the Hyracoidea. Their structure proclaims
these two divisions to be of ancient descent, and not to be modem
twigs of the Ungulate stem. As to the Perissodactyla and the
Artiodactyla we cannot bring them together nearer than in C[uite
early Tertiary times. The order Condylarthra seems to be the
starting-point of both these sub-divisions. JZugrotocfonia has been
considered to be an ancestor of the Perissodactyle branch, and
Protagonodon or Protoselene of the Artiodaetyla. If this be true,